Display device

ABSTRACT

A display device includes a flexible substrate including a first surface and a second surface facing the first surface; a TFT array layer provided on the first surface; a display element layer provided on the TFT array layer; a first heat releasing layer provided on the second surface; a first protective layer provided on the same side as the second surface; a second heat releasing layer provided on the display element layer; and a second protective layer provided on the display element layer. The second heat releasing layer has a light transmittance of 90% or higher.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2017-096268, filed on May 15,2017, the entire contents of which are incorporated herein by reference.

FIELD

An embodiment of the present invention relates to a display device, forexample, a flexible display device.

BACKGROUND

A display device is often produced to include a glass substrate. Theglass substrate is heavy and is easily broken when being subjected to animpact. Recently, a so-called flexible display device including aflexible substrate formed of, for example, a resin, which is lightweightand is not easily broken, is a target of attention. The flexible displaydevice is required to be durable against bending. For example, JapanesePatent No. 5791673 discloses a display device that is improved in thedurability against repeated bending and is bendable at a larger angle.

SUMMARY

An embodiment of the present invention is directed to a display deviceincluding a flexible substrate including a first surface and a secondsurface facing the first surface; a TFT array layer provided on thefirst surface; a display element layer provided on the TFT array layer;a first heat releasing layer provided on the second surface; a firstprotective layer provided on the same side as the second surface; asecond heat releasing layer provided on the display element layer; and asecond protective layer provided on the display element layer. Thesecond heat releasing layer has a light transmittance of 90% or higher.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view of a display device in oneembodiment according to the present invention;

FIG. 2 is a schematic plan view of the display device in the oneembodiment according to the present invention;

FIG. 3A is a schematic view of pixels that may be included in thedisplay device in the one embodiment according to the present invention;

FIG. 3B is a schematic view of pixels that may be included in thedisplay device in the one embodiment according to the present invention;

FIG. 3C is a schematic view of pixels that may be included in thedisplay device in the one embodiment according to the present invention;

FIG. 4 is a schematic cross-sectional view of the display device in theone embodiment according to the present invention;

FIG. 5 is a schematic cross-sectional view of the display device in theone embodiment according to the present invention;

FIG. 6 is a schematic cross-sectional view of the display device inanother embodiment according to the present invention;

FIG. 7 is a schematic perspective view of a display device in stillanother embodiment according to the present invention;

FIG. 8 is a schematic plan view of the display device in the stillanother embodiment according to the present invention;

FIG. 9 is a schematic cross-sectional view of the display device in thestill another embodiment according to the present invention;

FIG. 10 is a schematic cross-sectional view of the display device in thestill another embodiment according to the present invention;

FIG. 11A is a schematic cross-sectional view showing a step of a methodfor producing the display device in the still another embodimentaccording to the present invention;

FIG. 11B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 12A is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 12B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 13A is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 13B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 14A is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 14B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 15A is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 15B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention;

FIG. 16A is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention; and

FIG. 16B is a schematic cross-sectional view showing a step of themethod for producing the display device in the still another embodimentaccording to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings and the like. The present invention may becarried out in various forms, and is not to be construed as beinglimited to any of the following embodiments. In the drawings, componentsmay be shown schematically regarding the width, thickness, shape and thelike, instead of being shown in accordance with the actual sizes, forthe sake of clearer illustration. The drawings are merely examples anddo not limit the interpretations of the present invention in any way. Inthe specification and the drawings, components that have substantiallythe same functions as those described before with reference to aprevious drawing(s) bear the identical reference signs thereto (or theidentical reference signs with “a”, “b” or the like after the signs),and detailed descriptions thereof may be omitted. The terms “first”,“second” or the like provided for each of the components are used forthe sake of convenience in order to distinguish the components, and donot have any other significance unless otherwise specified.

In this specification, an expression that a component (first component)is “on” (or “above” or “below”) another component (second component)encompasses a case where such a component (first component) is incontact with the another component (second component) and also a casewhere such a component (first component) is above or below the anothercomponent (second component), namely, a case where still anothercomponent (third component) is provided between such a component (firstcomponent) and the another component (second component), unlessotherwise specified. In the following description, regarding across-sectional view, the side on which the TFT array layer is providedwith respect to a first substrate will be referred to as “above”, andthe opposite side will be referred to as “below” unless otherwisespecified.

In this specification, the first substrate (flexible substrate) includesat least one planar main surface, and layers including an insulatinglayer, a semiconductor layer and a conductive layer or elementsincluding a transistor, a display element and the like are provided onthe one main surface. In the following description, regarding across-sectional view, the one surface of the first substrate (flexiblesubstrate) will be used as the reference. Unless otherwise specified,the terms “upper layer”, “above” and “upper surface” used regarding thefirst substrate will be used with respect to the one main surface of thefirst substrate.

A flexible display device includes a plurality of layers provided in astacked manner. When being bent, the flexible display device receives abending moment. As a result, a surface of one layer is expanded, whereasa surface of another layer is contracted. There is also a face that isnot expanded or contracted, and such a face is referred to as, forexample, a neutral surface. When the flexible display device is bent,the layers farther from the neutral surface receive a stronger force ina tensile direction or in a compression direction. Upon receipt of heatgenerated in a display element displaying an image, external heat or thelike, the layers are, for example, thermally contracted or expanded. Asa result, the position of the neutral surface is changed. Such apositional change of the neutral surface breaks lines or transistorsincluded in the display device, or causes the layer including thedisplay element to be delaminated. This causes the image displayed bythe flexible display device to be darker or brighter, or causes a partof the image not to be displayed.

Some embodiments described below are directed to a flexible displaydevice provided in consideration of the position of the neutral surface.

Embodiment 1

A structure of a display device in an embodiment according to thepresent invention will be described.

FIG. 1 is a schematic perspective view of a display device 100 in oneembodiment according to the present invention. A display element layer198 includes display elements allowing the display device 100 to displayan image. The display elements are included in the pixels 120. Needlessto say, the display elements are included in a display layer 102.However, for easier understanding, FIG. 1 shows the display elementlayer 198 as being separated from a display layer 102.

The display device 100 includes the display layer 102 displaying animage. The display layer 102 is located on a first surface of a flexiblesubstrate 104. The display layer 102 is formed over both the TFT arraylayer 110 and the display element layer 198. The display layer 102includes a plurality of pixels 120 arrayed in one direction and anotherdirection crossing the one direction. A sealing layer 180 and a touchsensor layer 112 are provided as overlapping the display layer 102. Afirst heat releasing layer 310 and a first protective layer 312 areprovided on a second surface of the flexible substrate 104. In otherwords, the first protective layer 312 is located on the same side as thesecond surface of the flexible substrate 104 with respect to the displaylayer 102. A second heat releasing layer 322 and a second protectivelayer 324 are provided on an upper surface of the touch sensor layer112. Namely, in a region where the first heat releasing layer 310, thedisplay layer 102 and the second heat releasing layer 322 stack on eachother, the first heat releasing layer 310 is located below the displaylayer 102, and the second heat releasing layer 322 is located above thedisplay layer 102. Thicknesses of the first heat releasing layer 310,the second heat releasing layer 322, the first protective layer 312 andthe second protective layer 324 are adjusted such that the neutralsurface of the display device 100 is located in the vicinity of the TFTarray layer 110 and the display element layer 198. In other words, theneutral surface of the display device 100 is located in a layerincluding the TFT array layer 110 and the display element layer 198. TheTFT array layer 110 and the display element layer 198 may each bethinner than the flexible substrate 104. The first protective layer 312may be thinner than the second protective layer 324.

The above-described structure of the display device 100 allows the heatto escape efficiently and suppresses the position of the neutral surfaceof the display device 100 from being changed by the heat.

FIG. 1 further shows first terminals 212, second terminals 222, thirdterminals 122, an IC chip 124 and a scanning line driving circuit 126.The first terminals 212 and the second terminals 222 are supplied with atouch sensor signal via an external circuit (not shown). A touch sensorsignal is supplied to the touch sensor layer 112. The third terminals122 supply a signal to the pixels 120 via an external circuit (notshown). The IC chip 124 and the scanning signal driving circuit 126control the driving of the pixels 120.

FIG. 2 is a schematic plan view of the display device 100 in thisembodiment of the present invention. For easier understanding, FIG. 2shows the flexible substrate 104, the display layer 102 and the touchsensor layer 112. In actuality, the first heat releasing layer 310 andthe first protective layer 312 are located below the flexible substrate104, and the second heat releasing layer 322 and the second protectivelayer 324 are located above the touch sensor layer 112.

The TFT array layer 110 and the display element layer 198 are located onthe first surface of the flexible substrate 104. As described above, thedisplay layer 102 is formed over both the TFT array layer 110 and thedisplay element layer 198. The display layer 102 includes the pluralityof pixels 120. The IC chip 124 and the scanning signal driving circuit126 (FIG. 1) controlling the driving of the pixels 120 are located outerto the display layer 102. In this example, the scanning signal drivingcircuit 126 is located directly on the flexible substrate 104. Thepresent invention is not limited to this. For example, the scanningsignal driving circuit 126 may be provided on a substrate different fromthe flexible substrate 104 (e.g., on a semiconductor substrate, etc.).The substrate on which the scanning signal driving circuit 126 isprovided may be located on the flexible substrate 104 or a connector214. The scanning signal driving circuit 126 may control the pixels 120.Alternatively, a part of the scanning signal driving circuit 126 may beprovided on a substrate different from the flexible substrate 104, andthe substrate on which the part of the scanning signal driving circuit126 is provided may be located on the flexible substrate 104 or theconnector 214. Still alternatively, a driving circuit included in the ICchip 124, or a part of such a driving circuit, may be provided directlyon the flexible substrate 104.

The touch sensor layer 112 includes a plurality of first touchelectrodes 202 and a plurality of second touch electrodes 204. The touchsensor layer 112 may include a touch detection layer havingsubstantially the same size and substantially the same shape as those ofthe display layer 102. With such a structure, the touch sensor layer 112is allowed to be formed in a series of steps of forming the TFT arraylayer 110 and the display element layer 198. With such a structure, itis possible to provide the display device 100 having a so-called in-celltype touch sensor. The touch detection layer of the touch sensor layer112 is not limited to having such a structure. For example, the touchsensor layer 112 may be formed on another substrate so as to be smallerthan the flexible substrate 104 and larger than the display layer 102,and the display device 100 may be formed by bonding another substrate onwhich the touch sensor layer 112 is formed and the substrate 104 onwhich components other than the touch sensor layer 112 is formed. Insuch a case, the touch detection layer is in a region larger than thedisplay layer 102. Therefore, even when an end of the display layer 102is touched, the touch may be detected with high precision.

The first touch electrodes 202 are electrically connected with firstlines 206 extending from a region outer to the display layer 102. Thefirst lines 206 extend outer to the display layer 102 and areelectrically connected with first terminal lines 210 via contact holes208. The first terminal lines 210 are exposed in the vicinity of an endof the display device 100 to form the first terminals 212. The firstterminals 212 are electrically connected with the connector 214 such asa flexible printed circuit (FPC) substrate or the like. A touch sensorsignal is supplied to the first touch electrodes 202 from the externalcircuit (not shown) via the first terminals 212.

Similarly, the second touch electrodes 204 are electrically connectedwith second lines 216 extending from a region outer to the display layer102. The second lines 216 extend outer to the display layer 102 and areelectrically connected with second terminal lines 220 via contact holes218. The second terminal lines 220 are exposed in the vicinity of an endof the display device 100 to form the second terminals 222. The secondterminals 222 are electrically connected with the connector 214. A touchsensor signal is supplied to the second touch electrodes 204 from theexternal circuit (not shown) via the second terminals 222.

Although not shown, the display elements included in the display elementlayer 198 are, for example, light emitting elements or liquid crystalelements. The display elements are included in the pixels 120. In thedisplay layer 102, the plurality of display elements is arrayed in onedirection and another direction crossing the one direction. The TFTarray layer 110 includes a plurality of semiconductor elements, ofvarious types, controlling capacitances or the like included in thepixels 120, and a plurality of lines. The plurality of semiconductorelements of various types are, for example, transistors, capacitors, andresistors. The pixels 120 each include at least one display element, atleast one transistor and at least one line that are connected with eachother.

FIG. 3A, FIG. 3B and FIG. 3C are schematic views of the pixels 120included in the display device 100 in this embodiment of the presentinvention.

The pixels 120 each includes a plurality of sub pixels. For example, asshown in FIG. 3A, one pixel 120 includes a sub pixel 130, a sub pixel132 and a sub pixel 134. The sub pixels each include one display elementsuch as a light emitting element, a liquid crystal element or the like.The color provided by each sub pixel is determined by characteristics ofthe light emitting element or characteristics of a color filter providedon the sub pixel. In this specification and the claims, the pixels 120each include a plurality of sub pixels. The plurality of sub pixels eachinclude one display element and provide at least one color. The colorprovided by at least one of the plurality of sub pixels is differentfrom the color provided by at least one sub pixel among the other subpixels. The pixel 120 is the minimum unit that forms a part of an imagereproduced by the display layer 102. The sub pixels included in thedisplay layer 102 are each included in either one of the pixels 120.

In the array shown in FIG. 3A, the sub pixel 130, the sub pixel 132 andthe sub pixel 134 may be configured to provide different colors fromeach other. For example, the sub pixel 130, the sub pixel 132 and thesub pixel 134 may include light emitting elements respectively emittingred light, green light and blue light, which are the three primarycolors of light. A 256-level voltage or current may be provided to eachof the three sub pixels, so that the display device 100 providesfull-color display.

In the array shown in FIG. 3B, one pixel 120 includes two sub pixelsproviding different colors from each other. For example, one pixel 120may include the sub pixel 130 providing red and the sub pixel 132providing green, and another pixel 120 adjacent to the one pixel 120 mayinclude the sub pixel 134 providing blue and the pixel 132 providinggreen. In this case, two adjacent pixels 120 reproduce different colorranges from each other.

The sub pixels included in each pixel 120 do not need to have the samearea size with each other. For example, as shown in FIG. 3C, one subpixel may have a larger area size than that of each of the other two subpixels. In this case, for example, the sub pixel 134 providing blue maybe formed to have a larger area size, and the sub pixel 132 providinggreen and the sub pixel 130 providing red may be formed to have areasizes that are the same as each other and are smaller than that of thesub pixel 134.

FIG. 4 is a schematic cross-sectional view of the display device 100 inthis embodiment according to the present invention. FIG. 4 schematicallyshows a cross-section taken along line B1-B2 in FIG. 2

As shown in FIG. 4, the display device 100 in this embodiment accordingto the present invention includes the first protective layer 312, thefirst heat releasing layer 310, the flexible substrate 104, the TFTarray layer 110, the display element layer 198, the sealing layer 180,the touch sensor layer 112, the second heat releasing layer 322, and thesecond protective layer 324. The display layer 102 displaying an imageis formed over both the TFT array layer 110 and the display elementlayer 198. The first heat releasing layer 310 is located below thedisplay layer 102, and the second heat releasing layer 322 located abovethe display layer 102. As shown in FIG. 5, the display device 100 maynot include the touch sensor layer 112. In FIG. 4 and FIG. 5, thelayers, films and regions are shown as having substantially the samethickness as each other for easier understanding of the stack structureof the display device 100. In actuality, the first protective layer 312and the second protective layer 324 are thicker than the other layers,films and regions. The first heat releasing layer 310 and the secondheat releasing layer 322 are thicker than the other layers, films andregions although being thinner than the first protective layer 312 andthe second protective layer 324.

The thicknesses of the first heat releasing layer 310, the second heatreleasing layer 322, the first protective layer 312 and the secondprotective layer 324 are adjusted such that a neutral surface 116 of thedisplay device 100 is located in the vicinity of the TFT array layer 110and the display element layer 198. For example, the first heat releasinglayer 310 is made thinner than the second heat releasing layer 322, andthe first protective layer 312 is made thicker than the secondprotective layer 324. Where the thickness of a region below the neutralsurface 116 is “a” and the thickness of a region above the neutralsurface 116 is “b”, the neutral surface 116 is located such that a=b,namely, the neutral surface 116 is located in the vicinity of the TFTarray layer 110 and the display element layer 198 (in FIG. 4, theneutral surface 116 is included in the display element layer 198). Inother words, the neutral surface of the display device 100 is located ina layer including the TFT array layer 110 and the display element layer198.

The position of the neutral surface 116 may be represented by, forexample, expression 1 shown below. In expression 1, H is the height froma lower surface of the display device 100, Ei is the Young's modulus ofa material used to form the i'th layer from the lower surface of thedisplay device 100, and Ti is the thickness of the material used to formthe i'th layer. N is a positive integer of 1 or greater.

$\begin{matrix}{H = {\frac{1}{2} \times \frac{\sum\limits_{i = 1}^{N}{E_{i}\left( {T_{i}^{2} - T_{i - 1}^{2}} \right)}}{\sum\limits_{i = 1}^{N}{E_{i}\left( {T_{i} - T_{i - 1}} \right)}}}} & (1)\end{matrix}$

The position of the neutral surface 116 may be calculated based on thematerials of the layers included in the display device 100, thethicknesses thereof, and the like.

In a production process of the display device 100, the first heatreleasing layer 310, the second heat releasing layer 322, the firstprotective layer 312 and the second protective layer 324 may be bondedin a final step. The display device 100 having the above-describedstructure has the neutral surface 116 located in the vicinity of the TFTarray layer 110 and the display element layer 198, which have a directinfluence on the display device 100 when a part thereof is broken ordelaminated. With the above-described structure, the display device 100allows the thicknesses of the first heat releasing layer 310, the secondheat releasing layer 322, the first protective layer 312 and the secondprotective layer 324 to be adjusted easily.

With the above-described structure, even when the display device 100 isbent, the tensile stress and the compression stress applied to the TFTarray layer 110 and the display element layer 198 in the vicinity of theneutral surface 116 may be minimum. Therefore, in the display device100, the transistors or the capacitors included in the TFT array layer110 and the display element layer 198 in the vicinity of the neutralsurface 116 are prevented from being broken by the generated heat, orthe display elements are prevented from being delaminated by thegenerated heat. The display device 100 having the above-describedstructure allows the position of the neutral surface 116 to be adjustedand has a high level of durability against bending and a high level ofreliability against heat.

Embodiment 2

In this embodiment, another structure of the display device according tothe present invention will be described. Components same as those inembodiment 1 may not be described.

FIG. 6 is a schematic cross-sectional view of the display device 100 inthis embodiment according to the present invention. The display device100 shown in FIG. 6 is different from the display device 100 shown inFIG. 4 in the position of the touch sensor layer 112. Except for thispoint, the display device 100 in FIG. 6 is the same as that in FIG. 4,and the same components will not be described. In FIG. 6 also, thelayers, films and regions are shown as having substantially the samethickness for easier understanding of the stack structure of the displaydevice 100. In actuality, the first protective layer 312 and the secondprotective layer 324 are thicker than the other layers, films andregions. The first heat releasing layer 310 and the second heatreleasing layer 322 are thicker than the other layers, films and regionsalthough being thinner than the first protective layer 312 and thesecond protective layer 324.

The touch sensor layer 112 is located between the second heat releasinglayer 322 and the second protective layer 324.

In the display device 100 having such a structure, the second heatreleasing layer 322 is closer to the display element layer 198.Therefore, even if the display element layer 198 generates heat, thesecond heat releasing layer 322 allows the heat to escape easily.

Since the display element layer 198 and the second heat releasing layer322 are closer to each other, the second heat releasing layer 322 may bethinned so as to have a heat releasing characteristic equivalent to thatof the first heat releasing layer 310. In this case, the second heatreleasing layer 322 is more light-transmissive than the first heatreleasing layer 310. Alternatively, the second heat releasing layer 322may be formed of a material having a smaller thickness than, and has ahigher light transmittance than, the material of the first heatreleasing layer 310. The display device 100 having such a structureallows the position of the neutral surface 116 to be adjusted relativelyeasily and has a high luminance.

Since the display element layer 198 and the second heat releasing layer322 are closer to each other, the sealing layer 180 may be thinned. Itis preferred that the sealing layer 180 contains, for example, amaterial having a high heat conductivity. A material having a high heatconductivity is, for example, an inorganic insulating material such assilicon nitride (SiN) or the like. With such a structure of the displaydevice 100, the region below the neutral surface 116 and the regionabove the neutral surface 116 have equivalent heat releasingcharacteristics to each other.

In this embodiment, the first heat releasing layer 310, the second heatreleasing layer 322, the first protective layer 312, the secondprotective layer 324 and the touch sensor layer 112 may be bonded in afinal step. The display device 100 having the above-described structureallows the position of the neutral surface 116 to be adjusted easily.The display device 100 having the above-described structure has a highlevel of durability against bending and a high level of reliabilityagainst heat.

Embodiment 3

In this embodiment, still another structure of the display deviceaccording to the present invention will be described. Components same asthose in embodiment 1 and embodiment 2 may not be described.

FIG. 7 is a schematic perspective view of a display device 400 in oneembodiment according to the present invention. Like in embodiment 1, foreasier understanding, the display element layer 198 is shown as beingseparated from the display layer 102. The display element layer 198includes the display elements allowing the display device 400 to displayan image. The display elements are included in the pixels 120. Needlessto say, the display elements are included in the display layer 102.Unlike the display device 100 shown in FIG. 1, the display device 400shown in FIG. 7 does not include the touch sensor layer 112, andincludes the second heat releasing layer 322 located in a part of theregion of the display device 400. Except for these points, the displaydevice 400 shown in FIG. 7 is the same as the display device 100 shownin FIG. 1, and the same components will not be described. The displaydevice 400 may include the touch sensor layer 112. In such a case, thetouch sensor layer 112 may be located between the second heat releasinglayer 322 and the sealing layer 180 as shown in FIG. 4, or may belocated between the second protective layer 324 and the second heatreleasing layer 322 as shown in FIG. 6.

FIG. 8 is a schematic plan view of the display device 400 in thisembodiment according to the present invention. Unlike the display device100 shown in FIG. 2, the display device 400 shown in FIG. 8 does notinclude the touch sensor layer 112, and includes the second heatreleasing layer 322 located in a part of the region of the displaydevice 400. Except for these points, the display device 400 shown inFIG. 8 is the same as the display device 100 shown in FIG. 2, and thesame components will not be described. For easier understanding, FIG. 8shows the flexible substrate 104 and the display layer 102. Inactuality, the first heat releasing layer 310 and the first protectivelayer 312 are located below the flexible substrate 104, and the secondheat releasing layer 322 and the second protective layer 324 are locatedabove the display layer 102.

Although not shown, the display elements included in the display elementlayer 198 are, for example, light emitting elements or liquid crystalelements. The display elements are included in the pixels 120. In thedisplay layer 102, the plurality of display elements is arrayed in onedirection and another direction crossing the one direction. The TFTarray layer 110 includes various circuit elements controllingcapacitances or the like included in the pixels 120, a plurality oflines, and the like. The various circuit elements are, for example,transistors, capacitors, and resistors. The pixels 120 each include atleast one display element, at least one transistor and at least one linethat are connected with each other.

FIG. 9 is a schematic cross-sectional view of the display device 400 inthis embodiment according to the present invention. FIG. 9 schematicallyshows a cross-section taken along line B1-B2 in FIG. 8. Unlike thedisplay device 100 shown in FIG. 4, the display device 400 shown in FIG.9 does not include the touch sensor layer 112, and includes the secondheat releasing layer 322 provided in a part of the region of the displaydevice 400. Except for these points, the display device 400 shown inFIG. 9 is the same as the display device 100 shown in FIG. 4, and thesame components will not be described. In FIG. 9, the layers, films andregions are shown as having substantially the same thickness for easierunderstanding of the stack structure of the display device 400. Inactuality, the first protective layer 312 and the second protectivelayer 324 are thicker than the other layers, films and regions. Thefirst heat releasing layer 310 and the second heat releasing layer 322are thicker than the other layers, films and regions although beingthinner than the first protective layer 312 and the second protectivelayer 324.

As shown in FIG. 9, the neutral surface 116 is continuous in the planarregion of the display device 400. The second protective layer 324 coversthe second heat releasing layer 322. In the display device 400, thesecond heat releasing layer 322 is located only in a region that has ahigh temperature and easily generates heat when the display device 400is bent. An example of the region that easily generates heat is a heatgenerating component such as a battery or the like and the vicinitythereof. Another example of the region that easily generates heat is aregion that is bent highly frequently while the display device 400 isused. FIG. 9 shows an example in which the neutral surface 116 iscontinuous in the planar region of the display device 400. The neutralsurface 116 is not limited to this. The neutral surface 116 may beoffset between in a region where the second heat releasing layer 322 ispresent and in a region where the second heat releasing layer 322 isabsent. The thickness of a part of the second protective layer 324 thatis in the region where the second heat releasing layer 322 is absent maybe adjusted such that the neutral surface 116 is in the vicinity of theTFT array layer 110 and the display element layer 198. In other words,the neutral surface of the display device 100 is located in a layerincluding the TFT array layer 110 and the display element layer 198.

The first heat releasing layer 310 may also be located only in a regionthat easily generates heat. In this case, the first protective layer 312covers the first heat releasing layer 310. With such a structure, theneutral surface 116 is made continuous. However, it is preferred thatthe first heat releasing layer 310 is located in the entirety of theplanar region of the display device 400. A reason of this is that in thecase where the display device 400 is mounted on a mobile informationterminal or the like, a heat generating layer, for example, a layerincluding a battery or the like, is often located in the region belowthe flexible substrate 104, namely, in the region including the firstheat releasing layer 310.

The above-described structure of the display device 400 allows the totalvolume of the heat releasing layer layers 310 and 322 to be decreased.This decreases the production cost of the display device 400. Thedisplay device 100 having the above-described structure allows theposition of the neutral surface 116 to be adjusted and has a high levelof durability against bending and a high level of reliability againstheat.

Embodiment 4

In this embodiment, a method for producing the display device 100according to the present invention in the case where the display device100 is an organic electroluminescence display device will be described.Components same as those in embodiment 1 to embodiment 3 may not bedescribed.

A method for producing the display device 100 will be described withreference to FIG. 10 to FIG. 16B. FIG. 10 is a cross-sectional view ofthe display device 400 taken along line A1-A2 shown in FIG. 8. FIG. 11Ato FIG. 16B are each a cross-sectional view showing a step of the methodfor producing the display device 100. The cross-sections shown in FIG.11A to FIG. 16B correspond to the cross-section shown in FIG. 10. In thefollowing, regarding the structure of the plurality of sub pixels, thestructure of, generally, one sub pixel will be described for the sake ofsimplicity.

First, as shown in FIG. 11A, an underlying film 106 is formed on theflexible substrate 104. The flexible substrate 104 has a function ofsupporting the semiconductor elements, such as transistors 140 and thelike, included in the display layer 102 and also supporting the touchsensor layer 112, and the like. Therefore, the flexible substrate 104may be formed of a material that is resistant against the temperatureused to form the components to be formed thereon and is chemicallystable against the chemicals used in the formation of the components.Specifically, the flexible substrate 104 may contain a material selectedfrom glass, quartz, plastic materials, metal materials, ceramicmaterial, and polymer materials including polyimide, polyamide,polyester, polycarbonate and the like.

The flexible substrate 104 may be formed on a base member formed ofglass or the like. In this case, the base member on which the flexiblesubstrate 104 is formed is referred to also as a “support substrate”.The flexible substrate 104 may be formed by, for example, a printingmethod, a wet film formation method such as ink-jetting, spin-coating,dip-coating or the like, a lamination method or the like. In such acase, after the layers included in the display device 100 are formed onthe flexible substrate 104, the support substrate is peeled off from theinterface between the flexible substrate 104 and the support substrate.Thus, the display device 100 is made flexible. Alternatively, theflexible substrate 104 may be simply formed of any of theabove-described flexible materials with no use of the support substrate.Although not shown, the flexible substrate 104 may include a base memberformed of glass or the like, and an insulating film, a flexible film orthe like, that are bonded together by use of a viscous material such asan adhesive or the like.

The underlying film 106 has a function of preventing impurities such asan alkaline metal material or the like from being diffused from theflexible substrate 104 into the transistors 140 or the like. Theunderlying film 106 may contain silicon nitride, silicon oxide, siliconnitride oxide or silicon oxide nitride. The underlying film 106 isformed by chemical vapor deposition (CVD) or sputtering. The underlyingfilm 106 may be of a single layer or of a stack structure. In the casewhere the flexible substrate 104 has a low impurity concentration, theunderlying film 106 may not be provided, or may be provided to cover apart of the flexible substrate 104.

Next, a semiconductor film 142 is formed (FIG. 11A). The semiconductorfilm 142 may contain, for example, silicon. Alternatively, thesemiconductor film 142 may contain an oxide semiconductor. The oxidesemiconductor may be, for example, a mixed oxide of indium and gallium(IGO) or a mixed oxide containing indium, gallium and zinc (IGZO). Thesemiconductor film 142 may be single-crystalline, polycrystalline,microcrystalline, or amorphous.

In the case of containing silicon, the semiconductor film 142 may beformed by CVD by use of silane gas or the like as material gas. Theresultant amorphous silicon is heated or irradiated with laser light orthe like to be crystallized. In the case of containing an oxidesemiconductor, the semiconductor film 142 may be formed by sputtering orthe like.

Next, a gate insulating film 144 is formed to cover the semiconductorfilm 142 (FIG. 11A). The gate insulating film 144 may be of a singlelayer or of a stack structure. The gate insulating film 144 may beformed by substantially the same method as that of the underlying film106.

Next, a gate electrode 146 is formed on the gate insulating film 144 bysputtering or CVD (FIG. 11B). The gate electrode 146 is formed of ametal material such as titanium, aluminum, copper, molybdenum, tungsten,tantalum or the like, or an alloy thereof. The gate electrode 146 may beof a single layer or of a stack structure. For example, the gateelectrode 146 may have a structure in which a layer of a highlyconductive metal material such as aluminum, copper or the like issandwiched between layers of a metal material having a relatively highmelting point such as titanium tungsten, molybdenum or the like.

Next, an interlayer film 108 is formed on the gate electrode 146 (FIG.12A). The interlayer film 108 may be of a single layer or of a stackstructure. The interlayer film 108 may be formed by substantially thesame method as that of the underlying film 106. In the case where theinterlayer film 108 is of a stack structure, a layer containing anorganic compound may be formed and then a layer containing an inorganiccompound may be stacked thereon, for example. In the case where thesemiconductor film 142 contains silicon, after the gate electrode 146 isformed, the semiconductor film 142 may be doped with impurities ofphosphorus, boron or the like to form source/drain regions 142 b. Inthis step, a region where the gate electrode 146 and the semiconductorfilm 142 overlap each other becomes a channel region 142 a.

Next, the interlayer film 108 and the gate insulating film 144 areetched to form openings reaching the semiconductor film 142 (FIG. 12B).

Next, a metal film is formed to fill the openings to form source/drainelectrodes 148. In this embodiment, the first terminal line 210 isformed concurrently with the source/drain electrodes 148 (FIG. 12B).Therefore, the source/drain electrodes 148 and the first terminal line210 may be present in the same layer. The metal film may havesubstantially the same structure as that of the gate electrode 146, andmay be formed by substantially the same method as that of the gateelectrode 146.

Next, a flattening film 114 is formed to cover the source/drainelectrodes 148 and the first terminal line 210 (FIG. 13A). Theflattening film 114 has a function of absorbing concaved and convexedportions and inclining portions caused by the formation of thetransistors 140 and the first terminal line 210 to provide a flatsurface. The flattening film 114 may be formed of an organic insulatingmaterial. The organic insulating material may be, for example, a polymermaterial such as an epoxy resin, an acrylic resin, polyimide, polyamide,polyester, polycarbonate, polysiloxane or the like. The flattening film114 may be formed by, for example, a wet film formation method asdescribed above.

Next, an inorganic insulating film 150 is formed on the flattening film114 (FIG. 13A). The inorganic insulating film 150 acts as a protectivefilm for the transistors 140 and forms a capacitance (not shown)together with a first electrode 162 of a light emitting element 160 tobe formed later. Therefore, it is preferred that the inorganicinsulating film 150 is formed of a material having a relatively highdielectric constant. The inorganic insulating film 150 may be formed of,for example, silicon nitride, silicon nitride oxide or silicon oxidenitride. The inorganic insulating film 150 may be formed by CVD orsputtering.

Next, as shown in FIG. 13B, a contact hole 152, a contact hole 208 andan opening 154 are formed. Then, the first electrode 162, a connectionelectrode 234 and a connection electrode 236 are formed to fill thecontact hole 152, the contact hole 208 and the opening 154 (FIG. 14A).

The region where the connection electrode 236 is formed is, for example,the opening 154. In a later step, the opening 154, in which theconnection electrode 236 is formed, is to be a region where theconnection electrode 236 is connected with the connector 214 such as anFPC or the like via an anisotropic conductive film or the like.Therefore, the opening 154 is much larger than the region where theconnection electrode 234 is formed. The region where the connectionelectrode 234 is formed is, for example, the contact hole 208. The sizeof the opening 154 varies in accordance with, for example, the terminalpitch of the connector 214. For example, the opening 154 has a width of10 μm to 60 μm and a length of 1 mm to 2 mm. By contrast, it issufficient that the contact hole 208 has a size of approximately severalmicrometers by several micrometers to approximately several tenmicrometers to several ten micrometers at the minimum. There is a limiton the smallest possible size of the opening 154 due to the process ofmounting the connector 214. By contrast, the contact hole 208 may have aminimum possible size at which the conductive layers to be connected inthis region (in this example, the first line terminal 210, theconnection electrode 234 and the first line 206) are connected with eachother at a sufficiently low contact resistance.

In the case where light emitted by the light emitting element 160 is tobe extracted through a second electrode 166, the first electrode 162 isconfigured to reflect visible light. In this case, the first electrode162 contains a highly reflective metal material such as silver,aluminum, magnesium or the like, or an alloy thereof. For example, afilm of a light-transmissive conductive oxide is formed on the filmcontaining such a metal material or alloy. The light-transmissiveconductive oxide may be ITO, IZO or the like. In the case where thelight emitted by the light emitting element 160 is to be extractedthrough the first electrode 162, the first electrode 162 may be formedof a light-transmissive conductive oxide.

In this embodiment, the first electrode 162, the connection electrode234 and the connection electrode 236 are formed on the inorganicinsulating film 150. Therefore, for example, a film of any of theabove-described metal materials is formed to fill the contact hole 152,the contact hole 208 and the opening 154. Then, a film containing avisible light-transmissive conductive oxide is formed. These films areetched to form the first electrode 162, the connection electrode 234 andthe connection electrode 236. Alternatively, a film of the conductiveoxide, a film of any of the metal materials described above, the film ofthe conductive oxide may be sequentially stacked to fill the contacthole 152, the contact hole 208 and the opening 154, and then are etchedto form the first electrode 162, the connection electrode 234 and theconnection electrode 236. Still alternatively, a film of the conductiveoxide may be formed to fill the contact hole 152, the contact hole 208and the opening 154, and then a film of the conductive oxide, a film ofany of the metal materials described above, and a film of the conductiveoxide may be formed in a stacked manner to selectively fill the contacthole 152.

Next, a partition 168 is formed to cover an end of the first electrode162 (FIG. 14B). The partition 168 absorbs steps caused by the formationof the first electrode 162 and the like, and electrically insulates thefirst electrodes 162 in two adjacent sub pixels. The partition 168 isformed of an epoxy resin or an acrylic resin by a wet film formationmethod.

Next, a functional layer 164 of the light emitting element 160 and thesecond electrode 166 are formed to cover the first electrode 162 and thepartition 168 (FIG. 14B). The functional layer 164 mainly contains anorganic compound, and is formed by a wet film formation method such asink-jetting, spin-coating or the like, or a dry film formation methodsuch as vapor deposition or the like.

In the case where the light emitted by the light emitting element 160 isto be extracted through the first electrode 162, the second electrode166 may be formed of a metal material such as aluminum, magnesium,silver or the like, or an alloy thereof. In the case where the lightemitted by the light emitting element 160 is to be extracted through thesecond electrode 166, the second electrode 166 may be formed of alight-transmissive conductive oxide such as ITO, IZO or the like.Alternatively, the second electrode 166 may be formed of any of theabove-described metal materials with such a thickness that transmitsvisible light. In this case, a layer of a light-transmissive conductiveoxide may be further stacked on the layer of the metal material.

Next, the sealing layer 180 is formed. As shown in FIG. 15A, the sealinglayer 180 includes a first inorganic layer 182, an organic layer 184, asecond inorganic layer 186, and an organic layer 190. The firstinorganic layer 182 is formed to cover the light emitting element 160,the connection electrode 234 and the connection electrode 236. The firstinorganic layer 182 may contain, for example, silicon nitride, siliconoxide, silicon nitride oxide or silicon oxide nitride. The firstinorganic layer 182 may be formed by substantially the same method asthat of the underlying film 106.

Next, the organic layer 184 is formed (FIG. 15A). The organic layer 184may contain an organic resin such as an acrylic resin, polysiloxane,polyimide, polyester or the like. The organic layer 184 may be formed tohave such a thickness that an upper surface thereof is flat. It ispreferred that the organic layer 184 is selectively formed in the planarregion of the display layer 102. More specifically, it is preferred thatthe organic layer 184 is formed so as to overlap neither the connectionelectrode 234 nor the connection electrode 236. The organic layer 184may be formed by a wet film formation method such as ink-jetting or thelike. According to another method for forming the organic layer 184, anoligomer usable to form any of the above-described polymer materials maybe put into a mist-like or gas-like state under a low pressure andsprayed to the first inorganic layer 182, and then the oligomer may bepolymerized. The organic layer 184 may be formed also by this method.

Then, the second inorganic layer 186 is formed (FIG. 15A). The secondinorganic layer 186 may have substantially the same structure as thatof, and may be formed by substantially the same method as that of, thefirst inorganic layer 182. The second inorganic layer 186 may be formedto cover the connection electrode 234 and the connection electrode 236as well as the organic layer 184. As a result, the organic layer 184 issealed by the first inorganic layer 182 and the second inorganic layer186. This structure prevents entrance of moisture from outside. In thisembodiment, the sealing layer 180 has a three-film structure asdescribed above. Alternatively, the sealing layer 180 may include onlythe first inorganic layer 182, or two or more layers.

Next, the organic layer 190 is formed (FIG. 15B). The organic layer 190may contain substantially the same material as that of, and may beformed of substantially the same method as that of, the organic layer184 of the sealing layer 180. It is preferred that as shown in FIG. 15B,the organic layer 190 is formed selectively, more specifically, isformed in a region where the first inorganic layer 182 and the secondinorganic layer 186 contact each other. It is also preferred that theorganic layer 190 is formed so as to overlap neither the connectionelectrode 234 nor the connection electrode 236. Next, the organic layer190 is used as a mask to perform etching, so that a portion of the firstinorganic layer 182 and a portion of the second inorganic layer 186 thatare exposed from the organic layer 190 are removed (FIG. 16A). As aresult, the connection electrode 234 formed in the contact hole 208,which is located outside the display layer 102, is exposed. Theconnection electrode 236 formed in the opening 154, which is locatedoutside the display layer 102, is exposed. In this step, the inorganicinsulating film 150 may be partially etched away to be thinned.

As a result of the above-described process, the TFT array layer 110(FIG. 10), the display element layer 198 (FIG. 10), and the sealinglayer 180 (FIG. 10) are formed. The TFT array layer 110 and the displayelement layer 198 may each be thinner than the flexible substrate 104.

Then, the touch sensor layer 112 is formed. Specifically, the firsttouch electrode 202 is formed on the organic layer 190 (FIG. 16B). Inthis step, the second touch electrode 204 (FIG. 8) is formedconcurrently. The first touch electrode 202 and the second touchelectrode 204 may contain, as a main material, a light-transmissiveconductive oxide. The light-transmissive conductive oxide may be ITO,IZO or the like.

The first terminal line 206 is formed concurrently with the first touchelectrode 202 and the second touch electrode 204. The first terminalline 206 is formed to fill the contact hole 208. The first touchelectrode 202 and the first terminal line 206 are electrically connectedwith each other (FIG. 16B).

Next, an interlayer film 246 is formed on the first touch electrode 202and the second touch electrode 204 (FIG. 16B). The interlayer film 246may be formed of substantially the same material as that of, bysubstantially the same method as that of, the organic layer 184.

According to another method for forming the interlayer film 246, theinterlayer film 246 may be prepared in a sheet-like form, and then maybe bonded to cover the plurality of first touch electrodes 202 and theplurality of second touch electrodes 204.

As a result of the above-described process, the touch sensor layer 112is formed.

Then, an insulating film 266 (FIG. 10) is formed. The insulating film266 may contain a polymer material such as polyester, an epoxy resin, anacrylic resin or the like. The insulating film 266 may be formed by aprinting method, a lamination method or the like. In FIG. 10, theinsulating film 266 is of a single-layer. Alternatively, the insulatingfilm 266 may include two or more layers. Such a structure furtherimproves the degree of flatness and thus improves the strength of thedisplay device 100.

Although not shown, in the case where the flexible substrate 104 isprovided on the base member formed of glass or the like, the flexiblesubstrate 104 may be peeled off from the base member as follows, forexample. After the connector 214 is formed, light such as laser light orthe like is directed toward the flexible substrate 104, so that theadhesive force between the flexible substrate 104 and the base member isweakened. Thus, a physical force is used to peel off the flexiblesubstrate 104.

Then, the first heat releasing layer 310, the second heat releasinglayer 322, the first protective layer 312 and the second protectivelayer 324 are bonded to the structural body formed by theabove-described process. Although not shown, the bonding may be formedby use of a viscous material such as an adhesive or the like.

The first heat protective layer 312 and the second protective layer 324may each contain substantially the same polymer material as that of theinsulating film 266. The first protective 312 and the second protectivelayer 324 may each contain a polymer material such as polyolefin,polyimide or the like, as well as any of the above-described polymermaterials.

It is preferred that the first heat releasing layer 310 and the secondheat releasing layer 322 are each formed of a highly transparent andhighly heat-conductive material. Examples of such a material includecarbon-based materials such as graphite sheet, carbon nanotube and thelike, light-transmissive conductive materials such as indium tin oxideand the like, nanowires of aluminum (Al), silver (Ag) or an alloythereof, and the like. Especially, many types of graphite sheet arehighly heat-conductive. A display device in an embodiment according tothe present invention that uses a graphite sheet easily allows heat toescape easily and does not easily cause the position of the neutralsurface to be changed. In FIG. 10, the layers, films and regions areshown such that the stack structure of the display device 100 is easilyunderstood. In actuality, the first protective layer 312 and the secondprotective layer 324 are thicker than the other layers, films andregions. The first heat releasing layer 310 and the second heatreleasing layer 322 are thicker than the other layers, films and regionsalthough being thinner than the first protective layer 312 and thesecond protective layer 324.

In order to prevent damage caused when, for example, the display device100 is dropped or collides against something, it is preferred that thefirst protective layer 312 is thicker than the second protective layer324. Also, in order to distance the lower surface of the display device100 from a heat source such as the battery or the like, or in order toprevent the lower surface of the display device 100 from being directlysubjected to heat from the heat source, it is preferred that the firstprotective layer 312 is thicker than the second protective layer 324. Inthe case where the first protective layer 312 and the second protectivelayer 324 are to have such a thickness relationship, the thicknessesthereof may be adjusted such that the neutral surface 116 is notdisplaced from the vicinity of the TFT array layer 110 and the displayelement layer 198.

In the above-described description of the method for producing thedisplay device 100, the display device 100 is an organicelectroluminescence display device that causes light to be outputupward. It is preferred that the light transmittance of the second heatreleasing layer 322 is higher than that of the first heat releasinglayer 310. The light transmittance of the second heat releasing layer322 is preferably 90% or higher.

In the case where the display device 100 is mounted on a mobileinformation terminal or the like, a heat generating layer, for example,a layer including a battery, is often provided in the region below theflexible substrate 104, namely, in the region in which the first heatreleasing layer 310 is provided. Therefore, it is preferred that theheat conductivity of the first heat releasing layer 310 is higher thanthat of the second heat releasing layer 322. Specifically, where theheat conductivity of the first heat releasing layer 310 is k, it ispreferred that the heat conductivity of the second heat releasing layer322 is k×0.1 or higher and lower than k.

The display device 100 shown in FIG. 10 is produced by theabove-described method. The display device in an embodiment according tothe present invention produced in this manner has a structure in whichthe thicknesses of the heat releasing layers and the protective layersare easily adjustable such that the neutral surface is located in thevicinity of the TFT array layer and the display element layer. Thedisplay device in an embodiment according to the present invention, evenif being bent, minimizes the stress applied to the TFT array layer andthe display element layer in the vicinity of the neutral surface.Therefore, in the display device in an embodiment according to thepresent invention, the transistors and the capacitors included in theTFT array layer and the display element layer are prevented from beingbroken, and the display elements are prevented from being delaminated.

The display devices described above in the embodiments according to thepresent invention may have an element added thereto, or deletedtherefrom, or may be changed in design optionally by a person ofordinary skill in the art. The methods described above in embodimentsaccording to the present invention may have a step added thereto, ordeleted therefrom, or may be changed in the condition optionally by aperson of ordinary skill in the art. Such devices and methods areencompassed in the scope of the present invention as long as includingthe gist of the present invention. The above-described embodiments maybe optionally combined as long as no contradiction occurs.

In this specification, the description is mainly for the display device.The present invention is also applicable to any type of flat paneldisplays such as another type of self-light emitting display device, aliquid crystal display device, an electronic paper-type display deviceincluding an electrophoretic element and the like. The present inventionis also applicable to any size of display devices including small ormiddle-sized and large-sized display devices.

Even functions and effects that are different from those provided by theabove-described embodiments but are obvious from the description of thisspecification or are easily expectable by a person of ordinary skill inthe art are naturally construed as being provided by the presentinvention.

What is claimed is:
 1. A display device, comprising: a flexiblesubstrate including a first surface and a second surface facing thefirst surface; a TFT array layer provided on the first surface; adisplay element layer provided on the TFT array layer; a first heatreleasing layer provided on the second surface; a first protective layerprovided on the same side as the second surface; a second heat releasinglayer provided on the display element layer; and a second protectivelayer provided on the display element layer, wherein the second heatreleasing layer has a light transmittance of 90% or higher.
 2. Thedisplay device according to claim 1, wherein the first heat releasinglayer and the second heat releasing layer are provided between the firstprotective layer and the second protective layer.
 3. The display deviceaccording to claim 1, wherein the first protective layer, the first heatreleasing layer, the second heat releasing layer and the secondprotective layer are flexible.
 4. The display device according to claim3, wherein the display device has a neutral surface defined in a layerincluding the TFT array layer and the display element layer when beingbent.
 5. The display device according to claim 4, wherein the firstprotective layer is in contact with a surface, of the first heatreleasing layer provided on the second surface, that is opposite to thesecond surface.
 6. The display device according to claim 1, wherein theTFT array layer includes a plurality of transistors and a plurality oflines, the display element layer includes a plurality of displayelements, and each of the plurality of display elements is electricallyconnected with at least one of the plurality of transistors and at leastone of the plurality of lines.
 7. The display device according to claim1, wherein at least one of the first heat releasing layer and the secondheat releasing layer overlaps the display element layer.
 8. The displaydevice according to claim 1, further comprising a touch sensor layer. 9.The display device according to claim 6, wherein the display elementsare light emitting elements.
 10. The display device according to claim1, further comprising a sealing layer, wherein the sealing layer is incontact with the second heat releasing layer.
 11. The display deviceaccording to claim 10, wherein the sealing layer includes an inorganicinsulating film.
 12. The display device according to claim 1, whereinthe light transmittance of the second heat releasing layer is higherthan a light transmittance of the first heat releasing layer.
 13. Thedisplay device according to claim 1, wherein the TFT array layer and thedisplay element layer are each thinner than the flexible substrate, andthe first protective layer is thicker than the second protective layer.14. The display device according to claim 1, wherein the first heatreleasing layer has a heat conductivity higher than a heat conductivityof the second heat releasing layer.